This invention is concerned with the production of shaped, high polymeric articles; particularly, but not necessarily exclusively, it is concerned with the production of synthetic fibers or yarns.
An apparatus used in the production of synthetic yarns comprises a hopper unit containing a mixture of natural or unpigmented thermoplastic, high polymeric material usually in pellet form and a coloring agent. An extruder draws from said hopper unit and directs extrudate to a plurality of spinnerets producing yarn ends which are subsequently quenched and further processed.
Conventionally to produce high quality synthetic yarns of which the color is held constant to close tolerances the mixture contained in the hopper is produced in batches those batches being prepared by weighing the components of the mixture and then combining them. The mixture thus produced is then delivered to the hopper.
It is recognized that to produce lesser quality yarns the batch system of producing the mixture may be discarded in favor of a continuous process in which separate supplies of natural material and coloring agent are delivered directly to the hopper unit. In these arrangements a feed device usually in the form of a gate-like element, is provided in each supply, those devices each having separate control means and as the level of the mixture in the hopper falls those feed devices are opened to deliver natural material and coloring agent to bring up the level in the hopper.
While a continuously operating arrangement clearly is desirable over a batch production technique, as noted hereabove, it has been considered that such an arrangement can only be effective to produce lesser quality yarns. This conclusion finds its basis in the fact that the rates of flow through the feed devices vary appreciably with surface characteristics, shape, angle of repose and other factors so that the actual volumes of natural material and coloring agent delivered to the hopper may vary sufficiently from the amounts called for by the control means to produce substantial color variations.
According to this invention natural material is supplied to the hopper to maintain the level of material in the hopper and the supply of coloring agent to the hopper is controlled in dependence upon the throughput of the extruder. Thus, instead of attempting to make a mixture by controlling two feeds to the hopper each of which is subject to variations, one is, in effect, delivering into the hopper a feed of coloring agent which is related to the rate at which the mixture is being processed and since one is concerned with the amount of coloring agent in the extrudate and since the throughput is very accurately controllable, a much greater accuracy of color maintenance is achieved and high quality yarn is obtained on a continuous rather than batch basis.
Most desirably, the coloring agent is delivered to the hopper by continously operating feed means, the rate of operation varying only with variations in extruder throughput. In such an arrangement the feed means can, with good effect, be arranged to deliver the coloring agent in measured doses to the hopper, the interval between those doses being controlled in dependence upon extruder throughput.
Another problem with known continuous feed apparatus occurs when changes are made in the extruder throughput since obviously it is necessary to reset the coloring agent feed rate. Besides the adjustment of the feed rate of the coloring agent being of itself time consuming, it is to be understood that this adjustment occurs while the equipment is operating and, as such, until the adjustment is completed, that material being processed through the equipment is lost. Since, according to this invention, the coloring agent feed is matched to extruder throughput, this problem is avoided.